The invention concerns a method of continously converting hydrocarbons, in the presence of a catalyst, at a temperature of from 480.degree. to 600.degree. C., wherein an initial feedstock comprising hydrocarbons and hydrogen are circulated through at least two fluidized bed type reaction zones; the catalyst circulates through the reaction zone in the form of a fluidized bed, flowing continuously down said zone; it is then drawn off continuously from the bottom of the reaction zone and passed into a regenerating zone; the regenerated catalyst is sent into a zone for treatment with hydrogen, separate from the reaction zone, where it is treated at a temperature generally bellow the reaction temperature; after the hydrogen treatment the catalyst is passed continuously into a sulfurizing zone, separate from the hydrogen treatment zone and separate from the reaction zone; and after being treated with a sulphur compound, the catalyst flows continously to the reaction zone.
The invention more particularly concerns a method of hydro reforming hydrocarbons; the feedstock may be a naphtha distilling at from about 60.degree. to about 220.degree., particularly a direct distillation naphtha; it also concerns the production of aromatic hydrocarbons, for example the production of benzene, toluene and xylenes (ortho, meta or para), either from saturated or unsaturated gasolines (e.g., gasolines modified by cracking, particularly thermal cracking, or by catalytic reforming), or from naphthenic hydrocarbons which can be converted into aromatic hydrocarbons by dehydrogenation.
The feedstock circulates successively in each reactor or reaction zone in an axial or radial flow (that is, from center to periphery or from periphery to center). The reaction zones are arranged in series, side by side, so that the feedstock flows successively through each of them, with intermediate heating between zones; the fresh catalyst is introduced at the top of the first reaction zone where the fresh feedstock is introduced; it then flows continuously down that zone and is drawn off continuously at the bottom; any appropriate means (particularly a lift) is used to convey it to the top of the next reaction zone, in which it again flows down continuously, and so on to the last reaction zone, where it is drawn off continuously from the bottom, then passed into a regenerating zone.
The catalyst is circulated from the bottom of one reaction zone to the top of another, from the bottom of the last reaction zone to the regenerating zone and from the bottom of the regenerating zone to the top of the first reaction zone using any known elevating means. In the rest of the description and the claims, these means will be referred to as a "lift".
The solid which is displaced from one reaction zone to another and to the regenerating zone may, for example, be a granular catalyst. The catalyst may, for example, be in the form of spherical pellets generally from 1 to 3 mm and preferably from 1.5 to 2 mm in diameter, although the invention is not restricted to these values. The apparent density of the catalyst is generally from 0.4 to 1, preferably from 0.5 to 0.9 and more particularly from 0.55 to 0.8, although the invention is not restricted to these values.
The actual regeneration of the catalyst may be carried out by any known means. The catalyst is preferably subjected to:
(a) Combustion by means of a gas containing molecular oxygen;
(b) Oxychlorination by means of a gas containing molecular oxygen and simultaneously by means of a halogen or halogen compound, for example, a hydrohalic acid or an alkyl halide and;
(c) A final treatment by a gas containing molecular oxygen.
The three treatments are carried out either successively in a single fixed bed or in a fluidized bed, with the catalyst passing successively into three separate zones where each of the three regenerating stages are carried out.
Regeneration is followed by purging, for example with nitrogen, to eliminate any traces of residual gaseous oxygen from the catalyst.
Applicant's U.S. Pat. No. 4,172,027 describes several aspects of such a process. In particular, FIG. 1 of the present application corresponds to the prior art described in U.S. Pat. No. 4,172,027 corresponds to a method which is still currently used for the many advantages it offers.
In FIG. 1, which is given to illustrate prior art, purified hydrogen from the unit, which has been purified, is used as the lift gas. This so-called purified hydrogen may contain up to 10 volume percent or preferably 4% of various light hydrocarbons such as ethane and propane. It should be noted that methane is not considered as an impurity up to a volume equal to that of the hydrogen; this means that in this case, at the upper limit, the so-called purified hydrogen stream would contain 50 volume percent of methane.
The hydrogen from the unit can thus be used as it is as the lift gas, not only temporarily when the other hydrogen sources run out but also, after simple purification, as a hydrogen source throughout the whole reforming or aromatic hydrocarbon producing reaction, for hydrogen treatment of the regenerated catalyst and, when the regenerating zone is beside the first reactor, as a fluid providing the lift required to raise the catalyst above the first reactor after it has been regenerated and treated with hydrogen.
In FIG. 1 three reactors are used. The feedstock is introduced through the pipe 1, the furnace 2 and the line 3 into the first reactor 29. The effluent from the first reactor is drawn off through the pipe 30 and passed through the oven 37 and pipe 38 into the second reactor 42. The effluent from the second reactor is drawn off through the pipe 43 and passed through the oven 50 and pipe 51 into the third reactor 55. The effluent from the third reactor is drawn off through the pipe 56. When the unit is started up, the fresh catalyst is introduced through the pipe 4 in FIG. 1. The catalyst from the regenerating zone 10 enters the first reactor 29 through the pipes 27 and 28, in which it travels in the form of a fluidized bed. The catalyst is drawn off from the reactor 29 through a plurality of pipes such as 31 and 32 and through the pipe 33, through which it reaches the lift pot 34. This drawing off is a continuous process (a valve system is not essential), since the flow rate of the catalyst is regulated by an appropriate conventional control using hydrogen (pure or from the unit), which is injected through a pipe (not shown).
Enough gas is withdrawn from the unit to prevent part of the effluent from the reaction from being entrained with the particles of catalyst. The catalyst is then conveyed from the lift pot 34 to the second reactor 42 by any known elevating device, which will be referred to as a "lift" in this specification. As explained above, the lift fluid is advantageously recycled hydrogen or hydrogen produced by the unit and is introduced through the pipe 35. The catalyst thus conveyed in the lift 36 reaches the container 39, from which it reaches the second reactor 42 through a plurality of pipes such as 40 and 41. (The container 39 and pipes 40 and 41 could be an integral part of the reactor 42; that is they may be provided right inside the reactor. The catalyst passes through the reactor 42 in the form of a fluidized bed, is drawn off from it continuously as with the first reactor 29 through the plurality of pipes such as 44 and 45, and reaches the lift pot 47 through the pipe 46.
The catalyst passes through the lift 49, which may, e.g., be supplied with recycled hydrogen through the pipe 48. It reaches the container 52, from which it passes through the plurality of pipes such as 53 and 54 to arrive at the third fluidized bed reactor 55. The catalyst is drawn off continuously from the reactor 55 as it was from the first and second reactors 29 and 42, through the plurality of pipes 57 and 58; this exhausted catalyst reaches the lift pot 30 through the pipe 59. The exhausted catalyst is then sent into a "storage and settling" vessel 7 by means of the lift 6, which may be supplied with recycled hydrogen introduced through the pipe 61 into the lift pot 60. Passing through the valve system 8 (there are generally two valves about 10 to 15 cm in size on an industrial scale and the pipes 21 and 9, the exhausted catalyst reaches the regenerating zone 10. When it has been regenerated and purged therein, the catalyst passes through the lines 11 and 13 and the valve system 12 (there are again generally two valves about 10 to 15 cm in size) into the upper part of a tank 15. Purified hydrogen from the unit, is introduced into the tank 15 through the pipe 14 with preheating in the oven 5. The catalyst travels in the form of fluidized bed to the lower part or zone 26 of the tank 15; the regenerated catalyst is treated with hydrogen in the zone 26, using hydrogen introduced through the pipe 14. It moves within, zone 26 in the form of a fluidized bed.
In FIG. 1 the catalyst, which has been regenerated and treated with hydrogen, is drawn off continuously from the tank 15 through the pipe 16 and reaches the lift pot 17. From here, the catalyst carries continuously by hydrogen from the unit which is purified and introduced through the pipe 18 into the lift 19, to a receiving vessel 20 located above the first reactor 29 in FIG. 7. From the receiving vessel 20 the catalyst then flows continuously in the form of a fluidized bed through a plurality of pipes or "legs" such as 27 and 28, to the first reactor 29. Sulfurization, which takes place when the regenerated catalyst has been hydrogenated, is carried out partly in the lift pot 17, partly in the lift 19, and possibly partly in the vessel 20 and legs 27 and 28. The sulphur compound and possibly hydrogen (preferably hydrogen from the unit, purified) acting as a carrying gas for the sulphur compound, are fed into the lift pot 17 through the pipe 24.
The catalyst travels continuously within the zones 15, 17 and 20, the lift 19 and the associated pipes. This ensures that the hydrogen treatment and sulfurization temperatures are well regulated and avoids subjecting the catalyst to sudden temperature changes.
During the hydrogen treatment the excess hydrogen can be eliminated through the discharge pipe 22.
However, a layout of this type has some disadvantages due to the use of hydrogen as the lift gas (the gas used to lift the catalytic particles from a low to a high position, for example from the bottom of one reactor to the top of the next one, from the bottom of the last reactor to the top of the regenerating zone and from the bottom of the regenerating zone to the top of the first reactor). The disadvantage of using hydrogen is felt chiefly upstream and downstream of the regenerating zone (10). The regenerating zone must be free of any trace of hydrogen. So the hydrogen from the lift 6 which has brought the catalyst from the last reactor 55 to the regenerator has to be removed with effective purging and well upstream of the regenerating zone 10. Similarly, a hydrogen stream has to be re-established downstream of the regenerating zone, in order to drive the regenerated catalyst through the lift into the first reactor. These arrangements for protecting the regenerator from any trace of hydrogen at present require valves, e.g., 8, 8a, 12 and 12a in the drawing, which valves are currently fairly large (approximately 4 inches (10.16 cm) and are being replaced by 6 inch or 15.27 cm valves) due to the hydrogen pressures near the tank 15. FIG. 1 is simplified, showing two valves 8 and 8a and two valves 12 and 12a, though in reality there are five or six valves 4 or 6 inches in size upstream of the regenerator (10) and the same number downstream. Heretofore such valves have always posed specific manufacturing and safety problems.